"Depression is actually something that closely parallels or mimics low testosterone," said Brannigan. "So we see many men who have actually been treated clinically with antidepressants when in turn their underlying problem is low testosterone."

In many ways, testosterone is what makes men men, but as the body reaches middle age, levels will slowly drop by an estimated average of 1-2 percent per year.

Many are never really bothered by the change, but others can have problems.

Researchers are still trying to understand the long term health effects of low testosterone.

A rise in cases of low testosterone has some researchers scratching their heads.

"What we found which is interesting is that younger men have a much higher chance of having low testosterone then we thought about before," said Craig Niederberger of the University of Illinois at Chicago.

The reasons remain unclear, and what to do about it is also debatable - to learn to live with it or to take action.

Testosterone replacement therapy comes in many forms including patches, gels, implants and injections.

The marketing of these medications has exploded, but a recent medical journal review says treatment is questionable because it has risks and its efficacy is uncertain.

Brannigan says when taken in the prescribed doses, these treatments are generally safe and effective, but he stresses the therapy is not appropriate for all patients.

"For the patient where it's really interfering with the quality of life, I think sitting down with doc and having a discussion makes a lot of sense," said Brannigan.

Mike Andruzzi says treatment has changed his life. He has been doing testosterone replacement for a couple years now to help bring his levels to a more normal range. He says his energy level is up and so are his spirits.

"It doesn't make me feel better than the average person," said Andruzzi. "It makes me feel like the average person."

Guidelines were just revised on sex hormone treatments. The guidelines recommend against screening the general population.

The guidelines also say doctors should only make a diagnosis of low testosterone in men with consistent symptoms and signs and clear measurements of low levels.